Organic Chemistry (basics) Flashcards
What is a homologous series?
Series of organic compounds having the same functional group but with each successive member differing by CH2
What is a functional group?
Group of atoms responsible for characteristic reactions of a compound
What is a hydrocarbon?
Any compound containing only hydrogen and carbon
What is an aliphatic hydrocarbon?
A straight chained hydrocarbon which can be branched or unbranched
What is an alicyclic hydrocarbon?
Hydrocarbon with a non aromatic ring structure which can also be branched or unbranched
What is an aromatic hydrocarbon?
A hydrocarbon that contains at least one benzene ring
General formula example (decane)
CnH2n+2
Molecular formula example (decane)
C10H22
Empirical formula example (decane)
C5H11
Structural formula example (decane)
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
Skeletal formula example (decane)
/\/\/\/\/
What is an alkane?
A saturated hydrocarbon containing only C-H bonds
What is the general formula of an alkane?
CnH2n+2
What types of bonds do alkanes have?
Four sigma bonds, either C-H or C-C
What shape and bond angle do alkanes have?
Tetrahedral shape and 109.5* because every carbon atom is surrounded by 4 electron pairs and the shape is caused by the repulsion of these electrons
Why don’t alkanes have a fixed shape?
Because the sigma bonds act as axis for the atoms to rotate around freely
Why is fractional distillation possible in alkanes?
Because the boiling points of the alkanes differ
What are the rules for the boiling points of alkanes?
- Increases as chain length increases as the molecule has a larger surface area so there are more points of contact and so the London forces are stronger and b.p increases
- Decreases as branching increases as the molecules cannot pack together as closely so there are less points of contact which makes the London forces weaker and b.p decreases
Why are alkanes so unreactive?
- C-C and C-H sigma bonds are strong
- C-C bonds are non-polar
- Electronegativity of C and H is so similar
Why are alkanes used as fuel?
Because they are readily available and easy to transport
Can alkanes undergo combustion? If so, what do they produce?
In a plentiful supply of oxygen they can undergo complete combustion to produce CO2 and H20
Equation for butane undergoing combustion
2C4H10(g) + 1302(g) —–> 8CO2(g) + 10H20(g)
General equation for alkane complete combustion
CxHy + (x+y/4)02 —-> XCO2 + y/2H20
When does incomplete combustion occur?
When there is a limited of supply of oxygen
What products can be formed in incomplete combustion?
CO2 + H20 + CO (carbon dioxide) and/or C(soot)
Why is carbon monoxide so dangerous?
It is a colourless, odourless and highly toxic gas, which binds to haemoglobin more readily (higher affinity) than oxygen to form carboxyhaemoglobin. This prevents oxygen from being transported around the body so the victim suffocates to death.
What are structural isomers?
Compounds with the same molecular formula but a different structural formula
What type of reation is combustion?
Oxidation
What are the environmental impacts of soot being formed during incomplete combustion?
- Asthma
- Cancer
- Global dimming
What are the three ways structural isomers can be formed?
- Alkyl groups in different places
- Functional groups bonded to different parts
- Different functional groups
What are the two reactions alkanes can undergo?
- Radical substitution
- Combustion
Describe the sigma bond in an alkane
Sigma bond is a covalent bond which has a direct overlap of the electron clouds of bonding atoms
Why are alkanes insoluble?
Because the hydrogen bonds in water are stronger than London forces and alkanes contain no hydrogen bonds.
What is an addition reaction?
Where 2 reactants join to make 1 product
What is a subsitution reaction?
Where an atom or group of atoms is replaced by a different group of atoms
What is an elimination reaction?
Involved the removal of a smaller molecule from a larger one. 1 reactant molecule forms two products
What is heterolytic fission?
Where one bonding atom receives both electrons from the bonded pair
What is homolytic fission?
Where each bonding atom receives one electron from the bonded pair, forming two radicals
Why do we use radical subsitution?
Because alkanes are very unreactive but if we make radicals then we can get alkanes to react
What are the conditions for radical substitution?
UV light
What are the three main stages of radical substitution?
- Initiation
- Propogation
- Termination
What are the limitations of radical substitution?
- Further substitution (polysubstitution)
- Substitution at different carbons
What is an alkene?
An unsaturated hydrocarbon containing at least one C to C double bond, made up of one pi and one sigma bond
What is the angle around a C to C double bond?
120* because there are three regions of electron density around each carbon and these electrons repel each other
Why can’t alkenes rotate?
Because the p orbitals need to be able to interact and so the two carbon atoms are locked in place, either side of the double bond. This causes stereoisomerism to occur
What is stereoisomerism?
Compounds with the same structural formula but a different arrangement of atoms in space
Why are alkenes more reactive?
- High electron density of C to C double bond
- Pi bond is slightly easier to break
What is a radical?
Any species with an unpaired electron
Where is E/Z isomerism found?
Found in alkenes where both carbon atoms have 2 different groups attached
What is E isomerism?
When the highest priority groups are on opposite sides of the C to C double bond
What is Z isomerism?
When the highest priority groups are on the same side of the C to C double bond
What is cis/trans isomerism?
Should only be used when there are two hydrogen atoms and two non-hydrogen groups attached to to each carbon
Which letter does cis/trans correspond to?
Z - CIS (same)
E- TRANS (opposite)
What is an example of a molecule with cis/trans isomerism?
but-2-ene
Why doesn’t but-1ene have E/Z isomerism?
Because it doesn’t have two different groups attached to each carbon
How to work out the priority of a group?
Priority increases as atomic number increases
Why do some alkenes show E/Z isomerism?
Because of the restricted rotation about at least one bond due to too high an energy requirement
How to assign the priority of chains?
Move down each chain until there is a point of difference
What type of fission occurs in radical substitution?
Homolytic fission as radicals need to be formed
What reactions can alkenes undergo?
- Combustion
- Electrophilic addition
- Polymerisation
What is hydrogenation and what are the conditions?
- Alkene turns into an alkane
- Conditions are H2, Nickel Catalyst and 423K
What is halogenation and what are the conditions?
- Gaseous halogen
- This reaction can be used to test for unsaturation
- When bromine water is added to an alkene, if the colour disappears then a carbon double bond is present
What is hydration and what are the conditions?
- Alkenes turn into alcohols
- Conditions are steam and phosphoric acid catalyst
Alkene reaction with hydrogen halide and conditions
Reacts with gaseous hydrogen halides
How does a molecule with a non-polar bond act as if it is an electrophile?
- C to C double bond with high electron density induces temporary dipole in halogen molecule
- Partially positive atom is attracted to double bond
Why are there major and minor products formed in reactions?
Because each carbon in a chain has a different stability, depending upon which type of carbocation it is
What are the different types of carbocation?
- Tertiary, carbon is bonded to 3 alkyl groups
- Secondary, carbon is bonded to 2 alkyl groups
- Primary, carbon is bonded to 1 alkyl group
How does stability change dependent on the type of carbocation?
Primary , Secondary, Tertiary
—————————————>
stability
When are major and minor products formed?
Major products are products that are more likely to be formed by bonding to the more stable carbocation
Minor products are formed when they bond to a less stable carbocation
What is a nucleophile?
Electron pair donors
What is an electrophile?
Electron pair acceptors
What do curly arrows show in a mechanism?
Shows the movement of an electron pair
Why is recycling important?
-Reduces environmental impact by conserving fossil fuels and decreasing waste going to landfill
What is the basic process of recycling?
- Discarded polymers have to be sorted by type to prevent polymers being mixed
- Polymers are chopped into flasks, washed and dried then melted
- Recycled polymers are cut into pellets and used by manufacturers to make new products
Why is PVC recycling dangerous?
- Hazardous due to the high chlorine content (and range of other additives)
- Dumping them into landfill isn’t sustainable
- Burning them causes PVC to release hydrogen chloride (corrosive), CO2 (polluter) and CO (toxic)
What is the new method to recycle PVC safely?
- Uses solvents to dissolve to dissolve the polymer
- High grade PVC is then recovered by precipitation from the solvent and the solvent is reused again
How are waste polymers used for fuel?
- Waste polymers that have a high energy value from being derived from petroleum or natural gas
- These waste polymers can be incinerated to produce heat, generating steam to drive a turbine for electricity
What is feedstock recycling?
- Refers to a variety of chemical and thermal processes that can reclaim monomers, gases , or oil from waste polymers
- Materials can be used as raw materials for production of new polymers
- An advantage of this method is that it can handle unsorted and unwashed polymers
Why should we use biodegradable polymers?
- They can be broken down by microorganisms into water, CO2 and biological compounds
- They degrade and leave no visible or toxic residues
Where are biodegradable polymers being used?
- Supermarket bags made from plant starch can be used as bin liners for food waste so they can be composted together
- Compostable plates, cups and food trays from sugar cane fibres are replacing polystyrene
What are biodegradable plastics made out of?
Usually made from starch or cellulose
What are photodegradable polymers?
- Polymers that contain bonds that are weakened by absorbing light to start the degradation
- Alternatively, light-absorbing additives are used.
What are the requirements for hydrogen bonding?
- First molecule has hydrogen attached to a N, O or F
- Second molecule has a lone pair of electrons on a small, highly electronegative N, O or F atom
Does ethanal have hydrogen bonding?
Not on its own, but it does in water
What products can the oxidation of a primary alcohol form?
- Alcohol to Aldehyde
- Aldehyde to Carboxylic acid
- Water
What are the conditions of oxidation of a p alcohol to just an aldehyde?
- Distillation
- Potassium Dichromate/H2SO4
- 1 mole of oxidising agent [O]
What are the conditions of oxidation of a p alcohol to a carboxylic acid?
- Heating under reflux
- K2Cr2O7/H2SO4
- 2 moles of oxidising agent 2[O]
What products is formed from the oxidation of a secondary alcohol?
Ketone
Water
What are the conditions of oxidations of a s alcohol to a ketone?
- Heat under reflux
- K2Cr2O7/H2SO4
- 1 mole of oxidising agent [O]
Can tertiary alcohols be oxidised?
No because
What is the colour change?
-Orange to green
Why does distillation prevent further oxidation?
- Aldehydes have lower bp than alcohols
- Aldehydes will be evaporated and condensed down another tube to be collected
How does reflux allow further oxidation?
- Aldehyde formed vaporises and immediately condenses
- In Liebig condenser liquid returns to reaction so no substance is lost and is converted into a carboxylic acid
What does dehydration of an alcohol form?
Alcohol to Alkene
What does dehydration do?
Remove water
What are the conditions for dehydration?
- Phosphoric acid catalyst
- 160* C
- Need -OH and -H on adjacent carbon
What does the substitution of a metal halide of an alcohol form?
A haloalkane
What are the conditions for substitution of a metal halide?
Metal halide and sulfuric acid
What is the equation for substitution of a metal halide?
Alcohol +NaBr + H2SO4 —-> Haloalkane
What species are haloalkanes?
Electrophiles
How does substitution of a metal halide work?
- NaBr and H2SO4 react to form NaHSO4 and HBr
- HBr goes on to react with the alkane to form the haloalkane
What are some examples of nucelophiles?
- OH-
- H2O:
- NH3:
What type of reaction is the hydrolysis of haloalkanes?
Nucleophilic substitution
